Ciprofloxacin was obtained via the hospital pharmacy from Bayer Austria (400 mg/200 mL infusion solution). [14C]Ciprofloxacin (labeled in the 2-position of the quinoline ring, molar activity: 2.2 GBq/mmol, radiochemical purity: 98.2%) was obtained from Hartmann Analytic GmbH (Braunschweig, Germany). For the i.v. injection, [14C]ciprofloxacin (7 kBq, 1.1 µg) was dissolved in 10 mL of physiological saline solution and filtered through a sterile Millex-GS filter (0.22 µm; Millipore Corporation, Bedford, MA, USA).
No formal dosimetry calculation was performed for [14C]ciprofloxacin. Because of the very high sensitivity of AMS, the administration of only very low 14C amounts is required (7 kBq in the current study). In addition, as the energy of the β− particles emitted in the decay of 14C is relatively low (0.156476 MeV), AMS microdosing studies usually fall within risk category I (trivial risk, total effective dose < 0.1 mSv) according to the International Commission on Radiological Protection Publication 62 “Radiological Protection in Biomedical Research” [30 ]. However, an intravenously injected 18F-labeled radiotracer for PET (400 MBq) typically gives a total effective dose in the range of 5–10 mSv, corresponding to risk category IIb (minor to intermediate risk) in the International Commission on Radiological Protection publication 62 [30 ].
No formal dosimetry calculation was performed for [14C]ciprofloxacin. Because of the very high sensitivity of AMS, the administration of only very low 14C amounts is required (7 kBq in the current study). In addition, as the energy of the β− particles emitted in the decay of 14C is relatively low (0.156476 MeV), AMS microdosing studies usually fall within risk category I (trivial risk, total effective dose < 0.1 mSv) according to the International Commission on Radiological Protection Publication 62 “Radiological Protection in Biomedical Research” [30 ]. However, an intravenously injected 18F-labeled radiotracer for PET (400 MBq) typically gives a total effective dose in the range of 5–10 mSv, corresponding to risk category IIb (minor to intermediate risk) in the International Commission on Radiological Protection publication 62 [30 ].